Plated steel sheets are generally used after stamping. Therefore, as basic performances, it is required that the plating layer is hard to break and not easily peel off even when stamped. In general, a plated surface which becomes the outer surface of a can is easily damaged by stamping. This relates to the fact that, in the draw forming when forming the can, the sliding of the plated surface which becomes the outer surface of the can and a die is generally larger in comparison with the sliding of the plated surface which becomes the inner surface of the can and a punch.
In addition, in a Ni plated steel sheet which does not have a function of sacrificial protection from corrosion with respect to a steel sheet, reducing the exposure of the steel sheet as a substrate of plating even after processing is important in terms of improving the corrosion resistance after the stamping. Therefore, in Ni plated steel sheets, a technique of forming a Fe—Ni diffusion alloy layer on an interface of the steel sheet which is the base material and the Ni plating layer by performing a Ni plating process and then performing heating is known (for example, refer to Patent Document 1).
By forming the Fe—Ni diffusion alloy layer on the interface between the steel sheet and the Ni plating layer, it is possible to ensure high adhesion and, along with this, the Ni plating layer becomes a soft recrystallized Ni layer by annealing, whereby following the deformation of the steel sheet is easier during stamping and, as a result, excellent performances are exhibited such as being able to reduce the exposure of the Fe and also being able to eliminate bad influence of pin holes which are formed during the electroplating.
In addition, in a case where continuous stamping is performed in the industrial production, it is required that the die is not easily damaged as an important performance. In such a case, it is required that the plating surface which becomes the outer surface of the can be difficult to adhere to the die and have a high sliding ability. With respect to this demand, there is known a method where the adhesion to the die is suppressed by annealing a steel sheet where a Ni plating layer is formed, performing plating in a Ni plating bath where a gloss additive is added onto the Ni plating layer, and then forming a hard, glossy Ni plating layer on the surface layer. For example, in Patent Document 2, glossy Ni plating is performed on the uppermost layer of the surface which becomes the outer surface of the can. The glossy Ni plating layer is harder than an annealed recrystallized Ni layer or a matt Ni plating layer and the adhesion to the die during the stamping is reduced in comparison therewith.
In addition, Ni—W alloy plating is known as hard Ni based plating (for example, refer to Patent Document 3, Non-Patent Document 1, and the like). In general, Ni—W alloy plating is precipitated in an amorphous shape and is hard. In addition, Ni—W alloy plating is known to exhibit high hardness even when heated. Furthermore, since the NI—W alloy includes W with a high melting point, an alloy layer is not easily formed by solid phase diffusion. Since the new surface adheres less easily to the die for stamping than Ni even when exposed as long as there is a Ni—W alloy plating layer on the surface layer, it is possible to suppress the adhesion to a plated metal die and it is possible to increase productivity.